Dac that looks like something that should be in my garage!
JM, regular 90 weight gear oil from WalMart is fine, but I like #58304 Red Line 75W90 NS GL-5 Gear Oil because it's what Jay Leno puts in all his old transmissions to help them shift better and last longer.
Gear oil is sometimes like motor oil and football teams. Everyone has a favorite and there's not a ton of difference one way or the other.